The present invention relates to apparatus and methods for stacking paper, particularly fan-folded continuous forms exiting printers, in a reliable manner and which minimizes stacking failures.
Stacking fan-folded continuous forms, i.e., forms folded in a continuous Z configuration, has previously been accomplished by a variety of mechanisms. For example, certain mechanisms have utilized slipping puller rollers which pull the paper from the host printer, direct its travel through a guide throat, and feed the paper onto a vertically movable elevator tray. Typically, newly-fed paper is stacked directly on the top surface of the elevator tray. As the paper accumulates on the tray, each newly-fed fan-folded form is stacked and becomes the top of the accumulated stack. As the stack increases in height, the distance between the top of the stack to the exit area of the feed throat decreases. It has been recognized that this distance is critical for the stacking mechanism to function properly with respect to stacking fan-folded continuous forms and must be maintained within certain limits. This is conventionally accomplished by sensing the location of the top surface of the stack. When it reaches a predetermined height, the elevator tray is incrementally lowered to allow more paper to be fed on top of the previously accumulated paper. This cycle is successively repeated until there is no more paper to be stacked.
Stacking failures, however, occur with such mechanisms. For example, the top of the stack develops a U-shaped channel onto which newly-fed paper is directed. Two unique manifestations of such U-shaped channel may obtain. The first evolves as the stretched holes in the edges of tractor-fed forms prevent the sides of the forms from stacking as close to each other as the layers of the paper in the middle of the stack. A characteristic U-shaped channel forms along an axis perpendicular to the folds in the paper. The second manifestation develops as the bending resistance along the folds prevents the folded edges of the forms from stacking as close to each other as the middle portions of the forms. In this case, a U-shaped channel grows along an axis parallel to the folds in the paper. Both cases become more pronounced as the height of the accumulated paper stack increases. They also may occur in combination with one another. Additionally, the probability of stacking failure increases as the unevenness of the top of the stack increases.
According to the present invention, there is provided a unique paper stacking apparatus and method for stacking paper which minimizes stacking failures and maintains a relatively flat surface on which newly-fed forms are stacked by repeated compressions of the accumulated paper stack. Particularly, the stacking apparatus hereof includes a pair of opposed, generally L-shaped, elements or channels at the front and rear portions of the stacker and which elements extend lengthwise generally parallel to the folded edges of the paper to be stacked. Each element thus has a generally vertically extending guide and a generally horizontally extending support leg or surface. At the toe end of each support surface, a free-wheeling roller preferably spans the entire length of the element, the elements being disposed in facing relation to one another with a space or opening therebetween. The elements are pivotally carried by rods for swinging movement below the rods, the rods serving as the pivot axes for the elements. The rods are supported in movable slides which permit the distance between the elements to be adjusted to accommodate various form lengths. The elements have end plates with vertically extending slots at their upper ends for receiving the rods. Springs interconnect between the rods and end plates to bias the elements into lowermost positions. Additionally, the elements are configured to have centers of gravity such that the elements lie in an inclined position relative to one another, i.e., their support surfaces are inclined relative to one another. A paper support tray is mounted below the support elements and is movable vertically relative to the support elements.
To stack paper on the paper stacker hereof, the tray is lowered and several sheets of paper are fed and stacked on the tray in fan-folded configuration. The sheets are fed through the opening between the elements. The tray is then raised and the distance between the elements is adjusted by moving the slides which carry the pivot rods such that the elements are spaced a distance one from the other corresponding to the length of the form to be stacked. As the paper on the tray engages the depending toe rollers of the elements, the elements are pivoted into a first position with the support surfaces thereof extending generally horizontally and resting on the top sheet of paper on the elevator tray, the next sheet of paper to be stacked extending upward through the opening between the elements.
As paper is pulled into the stacker by a puller roller mechanism, the paper is stacked on the horizontal surfaces of the elements between the vertical guides of the elements and on top of the rollers at the toe ends of the elements. The rollers support the paper adjacent to but inwardly spaced from the edges of the paper near the fan-folds, while the center of the form rests on paper already fed onto the elevator tray below the elements. It will be appreciated that paper will continue to stack between the elements above the horizontal surfaces and rollers of the elements.
Upon sensing a predetermined height of paper stacked on the elements, for example, a stack about one inch high, a signal is provided. For example, an infrared light beam may shine across the width of the stacker and may be interrupted by the top of the one-inch stack of paper accumulated on the elements. At that time, the elevator tray is lowered by a timed duration of power to the tray motor. As the tray lowers, the elements pivot outwardly away from one another and from the edge folds of the paper. This occurs as a result of the centers of gravity of the elements being inward of their pivotal axes during stacking and as a result of the weight of the paper exerted on the toe rollers which, during stacking, is likewise inward of the pivot axes. Thus, the combined effect of lowering the elevator tray (hence removing the support which maintains the elements in their first position) and permitting the elements to pivot away from one another and the folds, causes the paper accumulated on the elements to drop past the elements onto the stack of paper accumulated on the elevator tray.
When tray lowering times out, the tray is raised. As the top of the accumulated stack on the tray reaches the elements, it engages the toe rollers. Upon further upward movement of the tray, the elements pivot inwards as the rollers roll toward the middle of the stack. Inward pivoting of the elements ceases when the bottom surfaces of the elements lie flat against the top of the stack of paper accumulated on the tray. Upward tray motion, however, continues to drive the elements upwardly against the bias of the springs at their pivot points. Thus, the paper accumulated on the tray is compressed between the tray and the bottom surfaces of the elements. When the top of the compressed paper stack blocks an infrared light beam and before the elements reach their mechanical limit of vertical travel, the tray is moved downwardly away from the elements by a timed duration of power to the tray motor. The tray thus moves to a lowered position and in which position the accumulated paper on the tray remains engaged with the rollers to maintain the support surfaces of the elements in their generally horizontal paper supporting first position. This enables another predetermined height of paper to be stacked on the elements whereupon the cycle is repeated until the paper supply has been completely stacked.
Accordingly, in one aspect of the present invention, there is provided apparatus for stacking fan-folded paper forms, comprising a frame, a form support tray carried by the frame, at least one form support element carried by the frame disposed above the form support tray for receiving forms to be stacked and means mounting the form support element on the frame for movement between a first position for supporting a plurality of fan-folded forms and a position for releasing the fan-folded forms for delivery onto and support by the tray.
In a still further aspect of the present invention, there is provided a method of stacking fan-folded forms exiting a printer comprising the steps of supporting a plurality of fan-folded forms above a support tray adjacent the printer exit and releasing the plurality of fan-folded forms above the support tray for delivery onto and support by the support tray.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for stacking fan-folded paper forms in a manner which, among other objectives, will reliably maintain the top of the accumulated paper stack flat by repeated compressions of the accumulated paper stack on the tray thereby minimizing or eliminating stacking failures resultant from uneven surfaces at the top of the accumulated stack.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.